Variation in deficient serum vitamin E levels and impact on assessment of the vitamin E status in horses

Abstract

A large fluctuation in normal serum vitamin E (alpha-tocopherol) concentrations (> 2 μg/ml) has been demonstrated in normal horses. The purpose of this study was to verify the fluctuation in serum vitamin E in horses with deficient levels (< 1.5 μg/ml) and to assess the diagnostic value of a single serum sample to determine the vitamin E status in a deficient horse. Serum vitamin E levels were monitored over a period of 24 hours in 6 normal horses and in 22 horses with clinical signs that may be related to vitamin E deficiency. The serum vitamin E levels varied widely within each horse, and the coefficient of variation (CV) was significantly larger in the deficient horses (mean CV: 41%), compared to the horses with normal levels (mean CV: 14%). In a small proportion of the deficient horses, the vitamin E levels varied from deficient to normal within 24 hours. The sensitivity of a single sample compared to the "true value" determined by the average of the samples, was 91%. The sensitivity in case of 2 serum samples increased to 97%. These findings suggest that a single serum value does not always provide reliable information about the true vitamin E status in a deficient horse and analyzing 2 serum samples allows a more accurate estimation of the vitamin E status. The conclusion therefore is that when a serum vitamin E value > 1.5 μg/ml is found in clinically suspected horses, a second serum sample should be evaluated.